std::ranges::adjacent_find
Defined in header <algorithm> |
||
|---|---|---|
| Call signature | ||
template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
std::indirect_binary_predicate<
std::projected<I, Proj>,
std::projected<I, Proj>> Pred = ranges::equal_to >
constexpr I adjacent_find( I first, S last, Pred pred = {}, Proj proj = {} ); |
(1) | (since C++20) |
template< ranges::forward_range R, class Proj = std::identity,
std::indirect_binary_predicate<
std::projected<ranges::iterator_t<R>, Proj>,
std::projected<ranges::iterator_t<R>, Proj>> Pred = ranges::equal_to >
constexpr ranges::borrowed_iterator_t<R>
adjacent_find( R&& r, Pred pred = {}, Proj proj = {} ); |
(2) | (since C++20) |
Searches the range [first, last) for two consecutive equal elements.
1) Elements are compared using
pred (after projecting with the projection
proj).
2) Same as
(1), but uses
r as the source range, as if using
ranges::begin(r) as
first and
ranges::end(r) as
last.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists may not be specified when calling any of them.
- None of them is visible to argument-dependent lookup.
- When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
| first, last | - | the range of elements to examine |
| r | - | the range of the elements to examine |
| pred | - | predicate to apply to the projected elements |
| proj | - | projection to apply to the elements |
Return value
An iterator to the first of the first pair of identical elements, that is, the first iterator it such that bool(std::invoke(pred, std::invoke(proj1, *it), std::invoke(proj, *(it + 1)))) is true.
If no such elements are found, an iterator equal to last is returned.
Complexity
Exactly min((result-first)+1, (last-first)-1) applications of the predicate and projection where result is the return value.
Possible implementation
struct adjacent_find_fn {
template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
std::indirect_binary_predicate<
std::projected<I, Proj>,
std::projected<I, Proj>> Pred = ranges::equal_to >
constexpr I operator()( I first, S last, Pred pred = {}, Proj proj = {} ) const
{
if (first == last) {
return first;
}
auto next = ranges::next(first);
for (; next != last; ++next, ++first) {
if (std::invoke(pred, std::invoke(proj, *first), std::invoke(proj, *next))) {
return first;
}
}
return first;
}
template< ranges::forward_range R, class Proj = std::identity,
std::indirect_binary_predicate<
std::projected<ranges::iterator_t<R>, Proj>,
std::projected<ranges::iterator_t<R>, Proj>> Pred = ranges::equal_to >
constexpr ranges::borrowed_iterator_t<R>
operator()( R&& r, Pred pred = {}, Proj proj = {} ) const
{
return (*this)(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj));
}
};
inline constexpr adjacent_find_fn adjacent_find;
|
Example
#include <algorithm>
#include <iostream>
#include <vector>
#include <functional>
int main()
{
std::vector<int> v1{0, 1, 2, 3, 40, 40, 41, 41, 5};
// ^^ ^^
namespace ranges = std::ranges;
auto i1 = ranges::adjacent_find(v1.begin(), v1.end());
if (i1 == v1.end()) {
std::cout << "No matching adjacent elements\n";
} else {
std::cout << "The first adjacent pair of equal elements is at ["
<< ranges::distance(v1.begin(), i1) << "] == " << *i1 << '\n';
}
auto i2 = ranges::adjacent_find(v1, ranges::greater());
if (i2 == v1.end()) {
std::cout << "The entire vector is sorted in ascending order\n";
} else {
std::cout << "The last element in the non-decreasing subsequence is at ["
<< ranges::distance(v1.begin(), i2) << "] == " << *i2 << '\n';
}
}
Output:
The first adjacent pair of equal elements is at [4] == 40 The last element in the non-decreasing subsequence is at [7] == 41
See also
|
(C++20)
|
removes consecutive duplicate elements in a range (niebloid) |
| finds the first two adjacent items that are equal (or satisfy a given predicate) (function template) |
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